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04 Mar 2015 8:27:49am

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Man made Co2-e is over and above natural CO2-e

What's driving the observed rate of warming is an accumulation of greenhouse gases in the atmosphere due to an imbalance in the carbon cycle. There was an equilibrium that evolved over time where the amount of carbon emitted from volcanoes, fires, Lake Nyalls etc. was absorbed by biological processes. The cycle of life and death, of photosynthesis, combustion and respiration kept atmospheric carbon at a fairly constant level, with changes in concentration occurring over centuries. Then humans figured out how to burn fossil fuels for energy, which brought in carbon from outside the carbon cycle (fossil fuels are buried and isolated from the processes that make up the carbon cycle). As these fuels were burned, more and more carbon was added to the system that it hadn't dealt with before. At the same time as this, natural carbon sinks like forests were (are) being cleared for farm land, timber and fuel. The disappearance of these carbon sinks means that the carbon cycle is less able to remove carbon from the atmosphere at the same time that more and more carbon is being added. Changes in atmospheric carbon concentrations are now happening over decades, rather than over centuries and millennia as happened under non-human influence.

The greenhouse gases that are being added to the atmosphere by fossil fuel burning, and not being removed due to disappearing sinks, change the wavelength of light as it passes through the atmosphere, trapping the light's energy as heat. This heat is observed as an increase in average global temperature, and is why 2001-2010 was the hottest decade on record and 1980 to 2010 was the hottest 30 year period on record. Like the increase in atmospheric carbon, the rate of increase in temperature is out of line with what has been observed in natural warming and cooling cycles.

There are multiple lines of evidence for this, from laboratory and field tests that show this happening, to measurements showing that the earth is warmer at night than it used to be, which shows an increase in stored heat, rather than changes in incoming energy (i.e. the 150k year Milankovitch cycles).

Once its in the atmosphere, CO2-e is CO2-e, whether it comes from a human, a cow or a volcano. However, the process that gets it into the atmosphere matters, as this determines what is driving the observed imbalance in the carbon cycle. Isotopic tests have shown conclusively that the increase in atmospheric CO2-e comes from human activity, while natural sources remain ~constant.